| Summary: | <p>In the last few decades, there is an increasing need to improve in situ
aerosol measurements. The improved measurements can provide a better
understanding of the role of atmospheric aerosol on the Earth climate
change. The improved measurement can also help to indicate the quality
of ambient air to prevent health problems caused by aerosol exposure.
Most in situ optically based aerosol photometer assume the refractive in-
dex of measured particles to give size-estimate. This type of instrument
can have a bias when measuring a particle whose refractive index is differ-
ent from the assumed value. SPARCLE was designed with two measure-
ment goals. First, SPARCLE measures both the size and refractive index
of a particle provided that the particle is a homogeneous sphere. Second,
SPARCLE is able to measure particles whose sizes range from 500 nm to
2,500 nm. This size range is within the range of the accumulation mode
of tropospheric size distribution.</p>
<p>The purpose of this work is to investigate the feasibility of SPARCLE.
A threshold level to detect particles was applied to differentiate between
background and scattering signals and it was found that applying the
threshold level can limit SPARCLE to detect particles smaller than 640 nm.
SPARCLE was calibrated using four monodisperse aerosols containing
Polystyrene latex (PSL) beads. The mean size of the aerosols are 1,100 nm,
1,800 nm, 2,000 nm and 3,000 nm. The refractive index of PSL is 1.59.
The results indicate that SPARCLE can measure the aerosols with the
deviation of the measured size and refractive index less than 2.2% and
1.05%, respectively, of the size and refractive index specified by the aerosol
manufacturers.</p>
<p>SPARCLE was used to measure a test aerosol. The test aerosol was
a mixture of water and liquid soap. The refractive index of the liquid
soap is 1.37. One of the main ingredient of the liquid soap is sodium
dodecyl sulphate whose the refractive index is 1.44. The refractive index
of the test aerosol measured by SPARCLE is 1.47. This value is close
to the refractive index of the sulphate suggesting that the test aerosol
was quickly dried and, then, a solid aerosol was formed which mainly
composed of the sulphate.</p>
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